From EP 0 175 352 B1 there is known a method and apparatus for rapid determination of the parameters of a sample medium. The apparatus is provided with a flow-through measuring cell for gases and fluids, which is suitable for simultaneous determination of a plurality of parameters, a transparent, luminescent sensor layer in the flow-through cell being in contact with the sample. The variables to be measured are oxygen concentration and temperature, the measured luminescence radiation having a wavelength of 650 nm, respectively 720 nm, while the excitation radiation has a shorter wavelength. Excitation is effected by means of LEDs and radiation detection by means of photodiodes, these elements being located on opposite sides of the flow-through measuring cell. Since the luminescent sensor layer is placed on the side of the detectors, the excitation radiation on its way to the luminescent layer must pass through the sample medium. In the case of absorbent fluids, such as blood, this is a disadvantage as the excitation radiation is appreciably attenuated by the medium to be measured.
From EP 1 130 382 B1 there is further known an optical sensor for the determination of a number of analytes in a fluid sample, where a plurality of optical sensors is in contact with the fluid sample. The arrangement comprises light sources providing excitation radiation and detectors for determining the light interaction by the sensors, and has a processor which evaluates the concentration of each analyte in the fluid sample from the measured light interaction. Among other purposes the sensor is used to measure glucose in blood with concomitant determination of O2 concentration and temperature.
There are also known measurement arrangements (EP 1 106 987 B1) in which both optical components (light source and detector) contact the sensor layer in the flow-through measuring cell on one and the same side, parts of the measuring cell being transparent and acting as light guides for the measuring radiation and excitation radiation.
From WO 2002/059585 A2 there is known a measurement arrangement for determination of the oxygen content of a gas, for instance breathing air. The measuring device comprises a flow-through measuring cell, in which is disposed a luminescence-optical sensor element in contact with the gas flow. Two reflection geometries are described as possible measuring geometries, where the radiation source for the excitation radiation and the detector receiving the luminescence radiation are located on the same side of the flow-through measuring cell. There is also described a transmitted-light geometry where the luminescence-optical sensor element is placed on the detector side of the flow-through measuring cell.